Scientists warn against premature predictions of a “substantial” El Niño

It’s too early to tell if the El Niño brewing in the Pacific will be a big event or how serious its impacts might be, scientists warned today.

Speaking at a press conference in London, scientists said they can’t rule out an El Niño as large as the one in 1997/8 – which raised global temperature by more than half a degree – but it’s looking unlikely.

There’s even a slight chance this year’s event could be a false alarm, say the scientists. But their best current guess is that we should expect a “moderate” event in the coming months.

Forecast

Tropical Pacific surface waters are warmer than average for this time of year, and have been for several months – a sure sign that El Niño is underway.

Average sea surface temperature anomalies for the week centered on 6 May 2015, relative to the 1981-2010 long term average. Source: NOAA Climate Prediction Centre ( CPC)

The latest forecast from the US National Oceanic and Atmospheric Administration (NOAA) gives a strong chance of a “weak to moderate” event lasting throughout the Northern Hemisphere summer.

During Spring, there’s still a lot of uncertainty about how El Niño could develop, and scientists are not ruling out the possibility of an event to rival the one the world experienced in the winter of 1997.

But based on current evidence, scientists are reasonably confident of a moderate strength event, Prof Adam Scaife, an expert on monthly and decadal prediction at the Met Office, told journalists today.

This would probably place this year’s event somewhere between the 1997/8 and the more recent 2009/10 event in terms of strength, said Scaife.

Most models suggest El Niño will remain through the end of 2015. Source: International Research Institute ( IRI)  

Overstatement

Today’s rather muted predictions contrast with last week’s flurry of headlines warning that a “substantial” El Niño event was underway.

The news reports were apparently prompted by comments from the head of forecasting at the Australian Bureau of Meteorology, following the agency’s latest forecast.

But Prof Eric Guilyardi, a climate scientist at the University of Reading, who was also at today’s press conference, suggests that level of confidence is unwarranted at this stage. He tells Carbon Brief:

“The adjective “substantial” is overstated at this time of the year (too early to say). The actual [Bureau of Meteorology] statement does not says so and is rightly careful. This adjective came from a media briefing, apparently.”

There’s even a small chance this year’s event could fizzle out to nothing, says Guilyardi. This time last year, scientists were confidently predicting an event, but it never materialised. He tells Carbon Brief:

“It is still possible that the event may die like last year, although the situation for this year looks more favourable as the atmosphere has reacted to the anomalously warm waters.”

Prof Mat Collins, joint Met Office chair in climate change at the University of Exeter, echoes Guilyardi’s caution, telling Carbon Brief:

“It is still only May and a lot can happen between now and the usual El Niño peak seasons in winter.”

But the climate model forecasts show better agreement this time round so the chances of a false alarm happening again this year are low, says Scaife.

Here’s the Met Office’s chief scientist Professor Dame Julia Slingo on El Niño’s surprising recent behaviour, and her thoughts about this year’s event.  This clip is part of an interview Carbon Brief carried out on 24 March 2015, you can see the full version here.

Hottest year

The ocean releases heat into the atmosphere during an El Niño, which tends to boost global temperatures. On top of the rising trend of greenhouse gases warming, an El Niño this year could well make 2015 the hottest year on record, the scientists said today.

The UK Met Office predicts global average temperature in 2015 will reach 0.64 degrees above the 1961-1990 long-term average. This is compared to 2014, which narrowly topped the charts with an average temperature of 0.57C above the long-term average.

Since the impacts of El Niño peak typically in December, the biggest boost to global temperature is likely to come in 2016, say the scientists.

Source: Rosamund Pearce, Carbon Brief.

Impacts

El Niño has some very serious impacts at smaller scales. It is typically associated with poor monsoons in Southeast Asia; droughts in Australia, Indonesia and the Philippines; heat waves in Brazil; and extreme flooding in Peru, Chile and Mexico, Guilyardi tells Carbon Brief.

Scientists are seeing some of these signals emerging, but things will become clearer in the next one-to-two months, says Scaife. The strongest impacts will come when El Niño reaches a peak in December.

But every El Niño is different, so predicting the scale of the impacts isn’t straightforward. Scaife also warns against overinterpreting the forecasts, saying:

“Every prediction is an expression of increasing or decreasing risk, there are no definitive predictions â?¦ Nothing is guaranteed”.

On longer timescales, climate change is expected to double the occurrence of extreme El Niño events, said the scientists. If emissions stay very high, the frequency of extreme events looks set to increase from one-in-six events now to one-in-three.

There is no evidence yet to say for sure whether the frequency or average strength of El Niño events will change as global temperature climbs higher, the scientists added.

Main image: Warm sea surface temperatures have caused foliose corals in the western Pacific to begin to bleach.